In the current technology for microcellular and dynamic polyurethane elastomer applications, the elastomer is prepared by the reaction of naphthalene diisocyanate (1,5-NDI) with an adipate ester polyol followed by chain extension with short chain diols, e. g. , 1,4-butanediol. The drawbacks of this elastomer technology are its inherently limited shelf stability and the need for processors to react monomeric isocyanate with a polyol on site. 1,5-NDI melts as high as 127.degree. C. ; therefore the reaction must take place above 130.degree. C. , a temperature which undesirable side reactions can occur promoting product instability. (Wirpsza, Z. , Polyurethanes Chemistry, Technology, and Applications, 1993, Ellis Horwood Limited, pp. 143.) The resultant prepolymer must then be extended within 30 minutes. This entire process requires significant capital investment in processing equipment due to the need for precise ratios of components, short shelf-life and the need to heat the materials to lower the viscosity for processing. Additionally, the system reacts very quickly allowing a very short working time, i. e. , pot life of 0. 5-5. 0 min.
Following the completed reaction, complex cure schedules and annealing processes are employed that are dependent upon the geometry of the parts. Annealing is completed by running several cycles at high temperatures (110.degree. C.) followed by room temperature cycling. This curing cycle can become quite rigorous and must be stringently followed in order to avoid shrinkage, undercure, and inferior physical properties. Deviation from this process results in significant final microcellular part inconsistency and an inability to meet the industry's desire for "Zero Defect" production and compromises quality.
In general, the expenses due to components, equipment, limited shelf-stability and processing of the NDI-based system pose serious drawbacks to its use. Health, safety, and environmental issues associated with the use of NDI are also of concern to the processors employing this technology.
In addition to the NDI-based system, other high viscosity isocyanate-terminated prepolymers, such as those based on MDI and polyester polyols, have been evaluated in elastomeric applications where specific dynamic and static physical properties are necessary. These consist of high viscosity isocyanate-terminated prepolymers that may offer a cost advantage over the NDI-based system; however, ease of processing is limited. A major concern with prepolymer-type systems is the loss of isocyanate functionality (loss of total NCO content) upon continued heating which, in turn, causes degradation of the system. Typically, stability of a prepolymer at a typical processing temperature of 85-90.degree. C. can be limited to only a few hours. (Wirpsza, Z. , Polyurethanes Chemistry, Technology, and Applications, 1993, Ellis Horwood Limited, pp. 142) This in turn causes a shift in stoichiometry (ratio of isocyanate to --OH and/or --NH.sub.2 groups) which requires a ratio adjustment. Without adjustment of the stoichiometry, the physical properties may be adversely affected, again resulting in inferior properties and inconsistent elastomer quality.
U. S. Pat. No. 4, 328, 322 discloses making synthetic polymers by the reaction of a polyisocyanate with substantially an equivalent of an oligomeric aminobenzoic acid ester or amide. Although directed to making cast elastomeric materials, the patent suggests that polymeric foams can be prepared by including any of a variety of blowing agents.
U. S. Pat. No. 4, 504, 648 discloses a polyurethaneurea comprising the polyaddition reaction product of polyisocyanate and a polyether polyol derivative having at least one terminal amino group in which at least one hydroxyl group is substituted by para-amino-benzoic acid ester. Example 7 shows the preparation of a cellular article having a density of 0. 086 g/cm.sup.3.
U. S. Pat. No. 4, 537, 945 discloses a poly(urethane)ureamide made by the reaction of a polyether polyol derivative and a polyisocyanate. Cellular products are suggested by incorporating a blowing agent into the reaction mixture, but no examples for making foam are provided.
U. S. Pat. No. 4, 732, 959 discloses a poly(urethane)ureamide made by the reaction of a polyester polyol derivative and a polyisocyanate. Example 8 shows the preparation of a soft foam sheet allegedly having a density of 0. 60 g/cm.sup.3.